linear algebra - Can somebody explain to me what 'void postConcat' in Android does? -

so have 2 matrices.

colormatrix , threshold. colormatrix initially,

c =  [  0.213 0.715 0.072 0 0;         0.213 0.715 0.072 0 0;         0.213 0.715 0.072 0 0;            0    0     0   1 0;] 

and threshold is:

t = [   255 0 0 1 -306;         0 255 0 1 -306;         0 0 255 1 -306;         0 0  0  1 -306;] 

now line of code in android colormatrix.postconcat(threshold); returns this:

c =  [  54.315 182.325 18.36 1 -306;         54.315 182.325 18.36 1 -306;         54.315 182.325 18.36 1 -306;            0      0      0   1   0; ] 

why? steps follows come result?

if same thing in matlab, c*t' this:

c =  [  54.315 182.325 18.36 0;         54.315 182.325 18.36 0;         54.315 182.325 18.36 0;            0      0      0   0; ] 

a different dimension array different values. can explain me postconcat does? can't find online function, in android documentation, , says this:

concat colormatrix specified postmatrix.  

. android thing?

why? steps follows come result?

the source code colormatrix can viewed here: https://android.googlesource.com/platform/frameworks/base/+/master/graphics/java/android/graphics/colormatrix.java

is android thing?

i believe kinda is, more colormatrix thing. in android, believe colormatrix provided way construct special colorfilter (colormatrixcolorfilter) used applied bitmap objects.

from colormatrix.postconcat description:

this logically same calling setconcat(postmatrix, this)

and description setconcat:

set colormatrix concatenation of 2 specified colormatrices, such resulting colormatrix has same effect applying matb , applying mata.

so, if understand correctly, believe colormatrix.postconcat can used combine 2 colormatrix objects 1 can apply once bitmap of choice instead of doing twice.

in short, if want have same behavior in matlab, might need implement yourself.